Liang J H, Nielsen G M, Lies D P, Burris R H, Roberts G P, Ludden P W
Department of Biochemistry, University of Wisconsin-Madison 53706.
J Bacteriol. 1991 Nov;173(21):6903-9. doi: 10.1128/jb.173.21.6903-6909.1991.
Reversible ADP-ribosylation of dinitrogenase reductase forms the basis of posttranslational regulation of nitrogenase activity in Rhodospirillum rubrum. This report describes the physiological effects of mutations in the genes encoding the enzymes that add and remove the ADP-ribosyl moiety. Mutants lacking a functional draT gene had no dinitrogenase reductase ADP-ribosyltransferase (DRAT, the draT gene product) activity in vitro and were incapable of modifying dinitrogenase reductase with ADP-ribose in vivo. Mutants lacking a functional draG gene had no dinitrogenase reductase-activating glycohydrolase (DRAG, the draG gene product) activity in vitro and were unable to remove ADP-ribose from the modified dinitrogenase reductase in vivo. Strains containing polar mutations in draT had no detectable DRAG activity in vitro, suggesting likely cotranscription of draT and draG. In strains containing draT and lacking a functional draG, dinitrogenase reductase accumulated in the active form under derepressing conditions but was rapidly ADP-ribosylated in response to conditions that cause inactivation. Detection of DRAT in these cells in vitro demonstrated that DRAT is itself subject to posttranslational regulation in vivo. Mutants affected in an open reading frame immediately downstream of draTG showed regulation of dinitrogenase reductase by ADP-ribosylation, although differences in the rates of ADP-ribosylation were apparent.
固氮酶还原酶的可逆 ADP 核糖基化构成了深红红螺菌中固氮酶活性翻译后调控的基础。本报告描述了编码添加和去除 ADP 核糖基部分的酶的基因突变的生理效应。缺乏功能性 draT 基因的突变体在体外没有固氮酶还原酶 ADP 核糖基转移酶（DRAT，draT 基因产物）活性，并且在体内不能用 ADP 核糖修饰固氮酶还原酶。缺乏功能性 draG 基因的突变体在体外没有固氮酶还原酶激活糖水解酶（DRAG，draG 基因产物）活性，并且在体内不能从修饰的固氮酶还原酶中去除 ADP 核糖。在 draT 中含有极性突变的菌株在体外没有可检测到的 DRAG 活性，这表明 draT 和 draG 可能共转录。在含有 draT 但缺乏功能性 draG 的菌株中，固氮酶还原酶在去阻遏条件下以活性形式积累，但在导致失活的条件下会迅速被 ADP 核糖基化。在这些细胞中体外检测到 DRAT 表明 DRAT 本身在体内受到翻译后调控。在 draTG 下游紧邻的一个开放阅读框中受影响的突变体显示出通过 ADP 核糖基化对固氮酶还原酶的调控，尽管 ADP 核糖基化速率存在明显差异。
